Characterization of nongxiang- and soy sauce-type distilled grains and their application in enhancing polyunsaturated fatty acid and triacylglyceride production from Chlorella sp. 038F

A sustainable method of handling large quantities of distilled grains in the Chinese baijiu industry is bioconverting these distilled grains into value-added products. We here compared the properties of two distilled grains, soy sauce-type (DGSB) and nongxiang-type (DGNB). Results revealed that DGSB had higher contents of crude protein, crude fat, soluble sugars, free amino acids, and antioxidants than DGNB. Mixotrophic cultivation of Chlorella sp. 038F was performed using aqueous crude extracts of distilled grains. Biomass, total lipid, and fatty acid production with DGSB crude extracts was approximately 2.43, 1.40, and 1.69 times higher than that with photoautotrophic culture, respectively, whereas DGNB crude extracts only improved the biomass by 1.64 times. Detailed profile analysis revealed that DGSB crude extracts remarkably increased the proportions of polyunsaturated fatty acids, especially linoleic and α-linolenic acids, and triacylglycerides in total lipids. Interestingly, DGNB crude extracts did not enhance total lipid accumulation but increased triacylglyceride accumulation. Comparative transcriptomics revealed that genes encoding photosynthetic pigments and proteins were downregulated, suggesting the decreased anabolism of the photosynthetic light reaction. Genes involved in fatty acid biosynthesis, the Calvin cycle, and glycolysis were upregulated, indicating sufficient accumulation of the building blocks acyl-CoA and glycerol-3-phosphate for triacylglyceride biosynthesis. All transcriptional trends of triacylglyceride biosynthesis-related genes were consistent with the triacylglyceride accumulation patterns. This study provides insights into the potential use of microalgae for the bioconversion of distilled grains into high-value products and highlights the role of distilled grains in improving polyunsaturated fatty acid and triacylglyceride production.